1. Field of the Invention
The present invention relates to a lens-fitted film unit, and more particularly to such a unit having a shutter device having a single swingable shutter blade of a kick-away type wherein one end portion of the blade is kicked away to open and close the shutter aperture.
2. Description of the Related Art
Inexpensive lens-fitted film units are sold widely. Such a unit has a film preloaded in the factory, and is returned to a photofinisher for development after all the frames have been exposed. The user is therefore not required to load the film or unload it after photographing.
A shutter device of the so-called kick-away type is used with such a lens-fitted film unit, as disclosed in U.S. Pat. No. 4,954,857 (corresponding to Japanese Patent Publ. (JP-B) No. 2-32615). In this shutter device, a single shutter blade is mounted swingably on a shutter base. The shutter blade is urged by a coil tension spring toward a closed position wherein the shutter aperture is light-shield. When photographing, the shutter button releases a cocked shutter drive lever. When the shutter drive lever is moved by a strong spring force, a kick-away arm of the shutter drive lever kicks away a claw of the shutter blade. The shutter blade then swings approximately at a constant speed against the relatively weak force of the coil tension spring to open the shutter aperture. When the shutter blade reaches the position wherein the shutter aperture is fully open, the kick-away arm rides over and passes the claw of the shutter blade. Thereafter, the shutter blade returns to the closed position by the force of the coil tension spring. The shutter blade is thus actuated at a fixed shutter speed, e.g. 1/125 second. The shutter drive lever is, in response to film winding, reset to the cocked position. The kick-away arm formed integrally with the shutter drive lever follows an arcuate path while it rides over and passes the claw.
In the process of manufacturing the same lens-fitted film unit, there is a step of inspecting its optical system. The lens as mounted is examined for eccentricity of position and the degree to which the optical axis of the lens departs from the intended optical axis. This inspection is carried out at an assembly stage wherein the main body of the film unit has been provided with a front cover attached thereto but has not yet been loaded with the film. Inspection light is shone on the lens and passes through it. The in-focus position of the inspection light is detected by a CCD sensor situated in an exposure station of the main body. To keep the shutter blade from hindering inspection, the shutter aperture is opened by actuating the shutter blade during inspection. There is, however, a problem in that such inspection is difficult. Even though utilized for lens inspection, the shutter device is adapted to actuate the shutter blade to open at a predetermined shutter speed, or for a predetermined duration suitable for taking a photograph. This limited duration of opening the shutter aperture is too short for the step of inspecting the lens.
For the manual assembly of the shutter device described above, the shutter blade 90 is formed with a hook 91 having a long sharp edge 91a as shown in FIG. 14 of the accompanying drawings. Since the hook 91 has such a long sharp edge 91a, the circular end portion 92a of the coil spring 92 is hard to disengage from the hook 91. For the automatic assembly of the shutter device described above, the shutter blade 90 is formed with a hook 93 with a short sharp edge as shown in FIG. 15, to allow an easy attachment of the end portion 92a of the coil spring 92 to the hook 93. In the case of the hook 91 with the long sharp edge 91a, it is necessary to expand the coil spring 92 over the sharp edge 91a of the hook 91 before coupling the end portion 92a to the hook 91. If this assembly operation is to be automatically preformed, it becomes very complicated. Therefore, the hook 91 is not suitable for the automatic assembly because of the difficulty of the assembly operation. For automatic assembly, however, the length A of the hook 93 is made smaller than the diameter B of the end portion 92a of the spring 92. Reference numeral 94 designates the shutter base, 95 the shutter cover.
In the case of the shutter device shown in FIG. 15 and assembled automatically, the end portion 92a of the coil spring 92 may disengage from the hook 93 when it receives an impact, because of the short length A of the hook 93. In the case of the shutter device shown in FIG. 14, and assembled manually, however, although the end portion 92a will not disengage from the hook 91 of the shutter blade 90, the other end portion 92b may disengage from a pin 96 under an impact.